The invention relates to a waste heat boiler that comprises, within a cylindrical jacket, a multiplicity of heat transfer pipes and a centrally arranged bypass pipe, each of which has an inlet end and an outlet end, and that comprises a control device to maintain the waste heat boiler gas exhaust temperature within a particular temperature range. The invention relates, in particular, to a waste heat boiler, the control device of which attaches to the outlet end of the bypass pipe in order to influence the waste heat boiler gas exhaust temperature.
Waste heat boilers that are fed on the pipe- and jacket side (channel side) with various gaseous and/or liquid mediums are used in numerous chemical and petrochemical processes. In the process, the hot exhaust gas that develops as a result of a process is fed to the heat transfer pipes, which are arranged as a pipe bundle within the waste heat boiler jacket, as well as to the bypass pipe. While passing through the heat transfer pipes, the hot exhaust gas transfers its heat to the cooling medium, generally water, on the jacket side and is subsequently removed from the waste heat boiler in a cooled state. In order to maintain the waste heat boiler gas exhaust temperature within a particular temperature range, it may be necessary to influence the exhaust temperature with the help of a controlled bypass. This may, for example, be accomplished by using a control damper or a rotating control damper or a control stopper that is arranged at the outlet end of the bypass pipe. Such control devices are known from printed publications DE AS 28 46 455 and EP 0 356 648 A1.
Because the exhaust gases in the bypass pipe of the waste heat boiler have a very high temperature and in the large majority of cases flow through at a high velocity, a control element such as a control damper or a control stopper that is arranged at the outlet end of the bypass pipe is subject to high thermal load. The control stoppers currently in use have the disadvantage that exhaust gases that flow out the outlet end of the opened bypass pipe form a powerful plume so that there is a danger of hot spots on the wall of the gas exhaust chamber. One or several of these hot spots cause thermal damage to the wall of the gas exhaust chamber, which in turn leads to undesirably short servicing intervals or to a shorter life span of the waste heat boiler.